Glaucoma is a progressive disease which leads to optic nerve damage, and, ultimately, total loss of vision. The causes of this disease have been the subject of extensive studies for many years, but are still not fully understood. The principal symptom of and/or risk factor for the disease is elevated intraocular pressure or ocular hypertension due to excess aqueous humor in the anterior chamber of the eye.
The reasons why aqueous humor accumulates are not fully understood. It is known that the elevated intraocular pressure ("IOP") can be at least partially controlled by administering drugs which reduce either the production of aqueous humor within the eye, such as beta-blockers and carbonic anhydrase inhibitors, or increase the flow of aqueous humor out of the eye, such as miotics and sympathomimetics.
All types of drugs currently being used to treat glaucoma have potentially serious side effects. Miotics such as pilocarpine can cause blurring of vision and other visual side effects, which may lead either to decreased patient compliance or to termination of therapy. Systemically administered carbonic anhydrase inhibitors can also cause serious side effects, such as nausea, dyspepsia, fatigue, and metabolic acidosis which can affect patient compliance and/or necessitate the withdrawal of treatment. Moreover, some beta-blockers have increasingly become associated with serious pulmonary side effects attributable to their effects on beta-2 receptors in pulmonary tissue. Sympathomimetics cause tachycardia, arrhythmia and hypertension. There is therefore a continuing need for therapies which control the elevated intraocular pressure associated with glaucoma.
Prostaglandins, which are metabolite derivatives of arachidonic acid, have recently been pursued for possible efficacy in lowering IOP. The arachidonic acid cascade is initiated by the conversion of arachidonic acid to prostaglandin G.sub.2 and subsequent conversion to prostaglandin H.sub.2. Other naturally occurring prostaglandins are derivatives of prostaglandin A number of different types of prostaglandins have been discovered including A, B, D, E, F and I-Series prostaglandins. Of interest in the present invention are combinations of compounds which exhibit similar IOP lowering mechanisms as PGD.sub.2, formula (I) and PGF.sub.2.alpha., formula (II): ##STR1##
The relationship between PGD.sub.2 receptor activation and IOP lowering effects is not well known. Various publications have reported that PGD.sub.2 receptor activation leads to second messenger activation and in particular, to the stimulation of adenylate cyclase and resultant increases in cAMP levels (Thierauch, Prostaglandins and their Receptors: II. Receptor Structure and Signal Transduction, Journal of Hypertension, volume 12, pages 1-5 (1994). Regardless of mechanism, PGD.sub.2 has been shown to lower IOP (Nakajima, Effects of Prostaglandin D.sub.2 and its analogue, BW245C, on Intraocular Pressure in Humans, Graefe's Archive Ophthalmology, volume 229, pages 411-413 (1991)). Thus, it has been of interest in the field to develop synthetic PGD.sub.2 analogues with IOP lowering efficacy.
Synthetic PGD.sub.2 -type analogs have been pursued in the art (Graefe's Archive Ophthalmology, volume 229, pages 411-413 (1991)). Though PGD.sub.2 -type molecules lower IOP, these types of molecules have also been associated with undesirable side effects resulting from topical ophthalmic dosing. Such effects have included an initial increase in IOP, conjuctival hyperemia, increases in microvascular permeability, and increases in eosinophile infiltration (Alm, The Potential of Prostaglandin Derivatives in Glaucoma Therapy, Current Opinion in Ophthalmology, volume 4, No. 11, pages 44-50 (1993)). The binding of other types of molecules with the PGD.sub.2 receptor may lead to IOP lowering effects, but with fewer or reduced side effects than the above mentioned PGD.sub.2 -type analogs.
The relationship of PGF.sub.2.alpha. receptor activation and IOP lowering effects is not well known. It is believed that PGF.sub.2.alpha. receptor activation leads to increased outflow of aqueous humor. Regardless of mechanism, PGF.sub.2.alpha. and analogs have been shown to lower IOP Giuffre, The Effects of Prostaglandin F.sub.2.alpha. the Human Eye, Graefe's Archive Ophthalmology, volume 222, pages 139-141 (1985); and Kerstetter et al., Prostaglandin F.sub.2.alpha. -1-Isopropylester Lowers Intraocular Pressure Without Decreasing Aqueous Humor Flow, American Journal of Ophthalmology, volume 105, pages 30-34 (1988)). Thus, it has been of interest in the field to develop synthetic PGF.sub.2.alpha. analogs with IOP lowering efficacy.
Synthetic PGF.sub.2.alpha. -type analogs have been pursued in the art (Graefe's Archive Ophthalmology, volume 229, pages 411-413 (1991)). Though PGF.sub.2.alpha. -type molecules lower IOP, these types of molecules have also been associated with undesirable side effects resulting from topical ophthalmic dosing. Such effects include an initial increase in IOP, breakdown of the blood aqueous barrier and conjunctival hyperemia (Alm, The Potential of Prostaglandin Derivatives in Glaucoma Therapy, Current Opinion in Ophthalmology, volume 4, No. 11, pages 44-50 (1993)). The binding of other types of molecules with the PGF.sub.2.alpha. receptor with other types of molecules may lead to IOP lowering effects, but with less side effects than those elicited by the above mentioned PGF.sub.2.alpha. -type analogs.
Based on the foregoing, a need exists for the development of molecules that will activate the PGD.sub.2 and PGF.sub.2.alpha. receptors, yielding a more efficacious lowering of IOP, while exhibiting fewer or reduced side effects.